1. Field of the Invention
This invention relates to reinforcing members suitable for use in rubber composite structures and more particularly to a heat treated steel reinforcing member containing an adhesive coating on the surface thereof.
2. Description of the Prior Art
Steel in the form monofilaments, viz ribbon or wire and strands or cords, are used for reinforcing rubber articles. It is well known that such reinforcing members exhibit certain mechanical properties, namely tensile strength and ductility, in order to be considered acceptable reinforcing components. Such properties can be attained by using a steel containing approximately 0.70% carbon. The combination of mechanical work imposed on the steel during fabrication and chemical analysis produces the desired properties in these steels.
Another technique for attaining comparable properties is to heat treat a steel alloy containing a lesser amount of carbon, for instance properly heat treating a steel containing about 0.50% carbon will yield a product having an ultimate tensile strength comparable to hard-drawn steel of 0.70% carbon.
In copending patent application Ser. No. 519,364, filed Oct. 30, 1974 by D. I. Golland, et. al., now U.S. Pat. No. 3,953,250, issued on Apr. 27, 1976, there is disclosed a method for producing a steel reinforcing member in the form of a monofilament. In another commonly assigned copending patent application Ser. No. 229,515, filed on Feb. 25, 1972 by M. R. Sargent et. al. there is disclosed a steel reinforcing member in the form of a twisted strand or cord. In order to attain the required properties in both the monofilament and the cord or strand construction these components must be heat treated. Such a heat treatment consists of austenitizing the steel member, quenching the steel member and thereafter tempering the steel member.
After the desired mechanical properties are obtained the monofilament or cord is coated with an adhesive in order for the reinforcing member to be used in the construction of a rubber composite. To insure satisfactory adhesion of the coating to the steel member a clean, uncontaminated steel surface is essential. Surface contamination can occur in several ways. For example, if oil is used as the quench media the heated steel member upon entering the quench can cause the quench to vaporize and result in a rather tenacious deposit of decomposed oil on the steel surface. Furthermore, oil is frequently applied to prevent rusting of the steel prior to the application of the adhesive coating and mill dirt naturally accumulates during routine handling of the steel as it is processed further contaminating the steel surface.
To achieve acceptable bonding of the adhesive to the steel surface the heretofore contamination had to be removed. Such contamination is generally removed by a complex and expensive cleaning cycle comprising alkali washing and a series of water and acid rinses. After cleaning the steel is then in a condition to receive the adhesive coating. Such a coating was applied by passing the steel member through an aqueous adhesive mixture. The coated product was then heated in order to dry and cure the applied adhesive.